1. Field of the Invention
The present invention relates to an improvement in a method of two-stage injection molding of an air conditioner outlet vent device that includes a synthetic resin housing, a plurality of synthetic resin blades, and a link, the blades being pivotably supported by the housing and disposed in parallel to each other within the housing, and the link operatively connecting the blades, wherein the plurality of blades are injection-molded in a secondary injection step subsequent to a primary injection step in which the housing is molded.
2. Description of the Related Art
Conventionally, such a two-stage injection molding method is already known from, for example, Japanese Patent Application Laid-open No. 6-166053.
As shown in FIG. 8, when injection-molding, in a secondary injection step, a plurality of blades 19 each integrally having a blade main body 22, a pair of support shafts 23 projecting from the blade main body 22, a pair of projections 24 projecting from the blade main body 22 at positions displaced to the rear of the support shafts 23, and a link shaft 25 having an axis parallel to the support shafts 23 and being connected to the two projections 24, in the above-mentioned conventional method, a gate 51′ is formed in a mold 42′ so as to inject a molten resin into a cavity 49 corresponding to the blade 19, in a portion corresponding to the rear edge of the blade main body 22 at a position away from the two projections 24.
However, when setting the position at which the molten resin is injected as described above, since the link shaft 25 is the last to be molded, there is a possibility that it might not be filled with sufficient molten resin resulting in an incomplete shape, or even if the external shape is molded, the resin density might be insufficient resulting in an inadequate strength.
In order to avoid such a situation, if an attempt is made to fill the portion corresponding to the link shaft 26 with sufficient molten resin, unnecessary filling pressure is exerted on portions other than the link shaft 25, thus causing the generation of flashing, or over-filling the interiors of shaft holes 21A and 21B of a housing 13 for the left and right support shafts 23 to make it difficult for the blades 19 to pivot. Furthermore, in the case where the injection speed for the blades 19 has to be increased in order to control the molding time for the blades 19 so as to synchronize it with molding of the housing 13 having a small volume, or in the case where a synthetic resin having a high injection speed such as PE, which has a low viscosity, is used, the surface of the blade 19 after completion of the two-stage injection-molding tends to have flow marks, etc., thereby degrading the surface appearance.
Moreover, if the molten resin is injected into the interior of the cavity 49 at a position away from the projections 24 as described above, a weld line tends to occur in a base part of the projections 24, and if talc, etc. is mixed with the molten resin in order to improve the rigidity of the blade 19, the weld strength of the base parts of the projections 24 might decrease resulting in that the strength of the link shaft 25 is not sufficient. Furthermore, since the diameter of a part of the gate 51′ through which the molten resin is injected into the cavity 49, and which corresponds to the blade main body 22, cannot be set greater than the thickness of the blade main body 22, the degrees of freedom in changing the gate diameter are limited.